Recently, a light source used in a thin film-type LCD TV is rapidly replaced by a light emitting diode (LED) having excellent energy efficiency and color expression in a conventional cold cathode fluorescent lamp (CCFL). The LED has various advantages such as high light conversion efficiency with respect to conventional CCFL (CCFL: 40%, LED maximum 90%), no mercury (environmentally-friendly), a fast response speed (60 nano seconds), a small size, and a long life span (50,000 to 100,000 hrs), it is widely used as a light source of a thin film-type TV.
However, one thing that is considered by related companies to mount an LED on a thin film-type TV is dissipation of heat generated from an LED chip. Recently, light emitting efficiency of the LED increases, but a heating value of the LED chip is on a considerable level, and thus if a suitable solution for heat dissipation is not found, a temperature of the LED chip increases too high, the LED chip itself or a packaging resin is degraded, and degradation of light emitting efficiency and decrease in lifespan of the LED chip are caused. Accordingly, to maintain a long life, which is the greatest advantage of the LED, it is essential to develop technology of heat dissipation for effectively dispersing heat generated from the LED chip.
To this end, various methods of increasing heat dissipating efficiency of the LED are discussed, but endeavor to reduce heat generated from the LED as much as possible by adding heat dissipation to a bottom chassis of a backlight unit (BLU) to which the LED chip is attached is accompanied. Particularly, ideas of the heat dissipation technology are also changed by which part of the bottom chassis has an LED lamp.
The LED backlight unit is broadly divided into a direct lighting type and an edge lighting type. The direct lighting-type backlight unit has LED lamps on a back side of a display which is seen by a person, and thus the LED lamps are evenly dispersed on an entire surface of the bottom chassis. Due to such a structural characteristics, in the direct lighting-type backlight unit, heat emitted from the LED is uniformly dispersed on the entire surface of the bottom chassis without being locally concentrated, and thus sufficient heat dissipation performance may be ensured only with an electro galvanizing (EG) anti-fingerprint steel sheet which is applied to a common LCD TV. However, the edge-type backlight unit is applied to high power LED and decreased in life span of a direct-circuit LED light source, and heat generated from the LED chip is concentrated on a side surface of the TV, thereby occurring thermal deformation of the bottom chassis. Now, as a method to solve this, application of an aluminum panel having excellent thermal conductivity as a material for the bottom chassis of a backlight unit, particularly, the edge-type backlight unit, or attachment of a heat dissipating pad and coating of a heat dissipating paint are performed.
Generally, since a thermal conductivity of aluminum is 200 W/m·K, which is more than or equal to double the thermal conductivity of steel, 80 W/m·K, local heat generated from the LED chip of the edge-type backlight unit is rapidly transferred to the entire bottom chassis, resulting in thermal balance. However, when the bottom chassis is applied as the aluminum panel, it consumes a part cost more than or equal to double the conventional material, an electro galvanizing anti-fingerprint steel sheet, and the aluminum panel is entirely dependent on imports. Therefore, as its use increases, due to the problem of supply of a raw material, the price may further increase. In addition, aluminum has a heat dissipation rate of approximately 0.02 to 0.25 according to a degree of alloy, and thus performance of emitting heat to an outside is considerably decreased, and workability is lower than that of steel, resulting in a high defect rate of 30% or more in a part processing process. Thus, the aluminum has several problems on aspects of physic properties such as corrosion resistance, workability and fingerprint resistance.
Meanwhile, since the general electro galvanizing anti-fingerprint steel sheet has a thermal conductivity of 60 to 65 W/m·K, which is very lower than the aluminum alloy plate having a thermal conductivity of 130 to 168 W/m·K, heat generated from the LED chip of an edge-type backlight unit has a limit to transfer heat to another part of the bottom chassis.
To solve the above-described problems, development of a resin composition for surface treatment which can maintain conventional fingerprint resistance and other physical properties, and enhance heat dissipation is eagerly demanded.